1. Field of the Invention
This invention relates to a radial tire for airplane, and more particularly to an airplane radial tire capable of establishing the high-speed durability and the weight reduction of the tire.
2. Description of the Related Art
The radial tire for airplane is defined to satisfy a basic internal pressure as very high as more than 10 atmospheric pressure as an official standard but also the reinforcing member for the tire is required to have a resistance top pressure corresponding to 4 times of the basic internal pressure in order to satisfy the requirement of higher reliability. In the belt of the tire, therefore, the resistance to pressure is satisfied by laminating many plies each comprised of organic fiber cords. On the other hand, it is imposed from airplane makers to satisfy the demand of significantly reducing the tire weight, and hence the establishment between the tire performances and the weight reduction is an important issue in the tire design.
The belt layer of the tire plays a hooping role for preventing the expansion of the tire crown portion in the radial direction, so that in order to efficiently obtain the resistance to pressure in the tire, it is preferable that the cords constituting the belt layer are arranged in parallel to an equatorial plane of the tire and are efficient to have a higher strength at breakage. From such a viewpoint, there is proposed a tire structure that organic fiber cord having a high strength at breakage is wound at an angle of approximately 0° with respect to the equatorial plane of the tire (see JP-A-63-4950).
This tire is excellent in the hoop effect and can effectively prevent the expansion of the tire crown portion. However, aramid fiber cord widely used as a constitutional member of the tire is poor in the heat shrinking property. Therefore, it is difficult to completely correct a slight non-uniformity of the strength between the cords generated in the shaping of the tire at a tire vulcanization step, and hence it is difficult to equally apply tension to belt cords in the pressure test for measuring the safety ratio of the tire. Since the utilization ratio of the strength in the tire member is low, it is required to arrange the excessive number of the members for satisfying the desired resistance to pressure though the strength at breakage of the member is high. Thus, the above cord property in the conventional tire product obstructs the weight reduction of the tire.
Also, standing wave is caused in the vicinity of the sidewall during the high-speed rotation of the tire to promote heat generation in the side portion, which considerably damages the durability of the tire. In order to prevent this problem, there is known that it is effective to increase tension in the circumferential direction of the belt at the shoulder portion of the tire during the running. For this end, the aramid fiber cords are usually used in the belt. In the belt, however, it is difficult to uniformly bear the tension between the cords as previously mentioned, so that it is also required to arrange the excessive number of the members for preventing the standing wave.